The present invention relates a motor vehicle tire designed to be inflated but capable of operating satisfactorily over long distances without inflation. More particularly it relates to a self-supporting tire for motor-vehicle wheels incorporating elastic support inserts in the sidewalls, comprising a carcass, a tread band disposed on the crown of said carcass, and a circumferentially-inextensible annular belt structure, overlying said carcass so as to form an annulus at a radially inner position to said tread band, that is, sandwiched between the carcass and the tread band. More particularly, the invention comprises the combination of: a pair of circumferentially inextensible reinforcing rings or bead cores, each positioned within in a bead defined along an inner circumferential edge of a tire; a pair of elastomeric fillers each of which extends along an outer circumferential edge of one of the bead cores tapering away from the tire axis; at least one carcass ply having its edges folded back around the bead cores and elastomeric fillers; at least a pair of annular elastic support inserts of lenticular cross-sectional form, made of elastomeric material, each of which is applied to the carcass ply against the inner part of one of the tire sidewalls extending radially between one of the beads and the corresponding edge of the belt structure.
It is known that there are motor-vehicle tires provided with a self-supporting carcass, that is capable of supporting the vertical loads and side thrusts transmitted to the tire even when it is operated under completely deflated conditions. In this way, in case of puncture of one or more tires, the motor-vehicle will be still able to travel over rather long distances even at relatively high speeds, without important losses occurring in terms of road-holding and ride comfort.
One known type of self-supporting carcass substantially provides that an annular support insert of lenticular cross-sectional form and made of elastomeric material be associated with each of the tire sidewalls, said insert being applied to the carcass ply or plies which, as known, are provided in the tire itself. These inserts having relatively high thickness and modulus of elasticity, are adapted to bend so as to offer sufficient elastic reaction to the vertical loads and horizontal side thrusts transmitted to the tire in a deflated condition.
In order to enable elastomeric inserts of smaller thickness and lower modulus of elasticity to be used, so as to improve the ride comfort and reduce the heat generation within the tire, according to another known type of self-supporting carcass each of the tire sidewalls is provided with two annular elastomeric support inserts disposed in side by side relation with respect to each other, at least one of which is interposed between two carcass plies.
The applicant has recently studied and set up another type of self-supporting carcass as described in the published European Patent Application EP-475258 which corresponds to allowed U.S. application 07/760,394, filed Sep. 16, 1991, now U.S. Pat. No. 5,238,040, in which, for each tire sidewall, an annular elastic support insert is provided which is positioned within the sidewall, against a first carcass ply. Combined with this elastic support insert is a pair of annular reinforcing inserts disposed substantially in radial alignment relationship between the first carcass ply and a second carcass ply laid on top (radially and axially outward) of the first ply. The reinforcing inserts are consecutively connected to each other at a junction point located at the height of the maximum-thickness area of the support insert and substantially coincident with the maximum-chord point of the tire.
During tire use the elastic support insert is deformed in the presence of bending stresses in order to elastically counteract the mutual approaching of the reinforcing inserts that substantially behave as stiff arms mutually hinged at their junction point.
In accordance with the present invention it has been found that by providing the elastic support insert with a substantially stiff core occupying at least the maximum-chord point of the tire, and more exactly the area in which compressive deformations are greatly concentrated, an important increase in the carcass lift under deflated conditions of the tire is achieved. Thus according to the invention very soft materials may be used for making the remaining part (other than the core) of the support insert, so as to greatly improve the ride comfort under any use condition.